Conventional Compaction Research Articles

Experimental Study on Forming Underground Space in Soil Using Explosive Lining Method

Explosive lining is a new method to construct underground space in soil. By making the most of compressibility of soil and thixotropy of concrete under explosive loading, this method offers an efficient path to form a cavity and its concrete support layer synchronously. In order to investigate the forming effect, a series of contrastive laboratory tests, including explosive lining method and conventional explosive compaction method, were performed under same soil and explosive conditions. Results show that measured dynamic stress and displacement by explosive lining method are higher than that of by conventional explosive compaction method under same equivalent radius, and the range of compact region in soil is larger too. Similarly, the physical and mechanical performance indexes of soil, such as water content and cohesion are superior to that of by conventional explosive compaction. It is approved that an even thickness concrete support layer can be formed in one-shot forming process by explosive lining, and there is no evident cranny region in the soil around the cavity.

Fabrication of High Density Y<sub>2</sub>O<sub>3</sub> Ceramics by Magnetic Pulsed Compaction

Highly dense Y2O3 ceramics have been fabricated by a magnetic pulsed compaction (MPC) which is capable of reaching a sufficiently high pressure (~1GPa) in a very short duration (a few microseconds), and a subsequent pressureless sintering at 1600°C. The Y2O3 green bodies with a relative density of about 68% were achieved by the application of the MPC process due to the effect of an enhanced rearrangement and a high speed movement of the particles, without the help of ceramic binder. Those compacts showed densities greater than 95%, which is very close to the theoretical density, after the subsequent pressureless sintering process at 1600 oC. The shrinkage rates of the diameter for the samples compacted by the MPC process were markedly reduced, when compared to those for the ones by the conventional compaction (CC) process.

Melt densification of radioactive plastic wastes

Volume reduction studies were carried out on low level radioactive plastic wastes containing polyethylene, PVC and neoprene by melt densification. The optimized temperature for melting of plastics was between 170 and 180 °C. Based on laboratory scale studies. Plant scale studies were planned and conducted. The volume reduction factors obtained were around 30, which was 6-10 times higher than that of the conventional compaction process. Thermogravimetry and infrared spectroscopy were used to investigate the thermal and structural properties of the given materials. The effect of the presence of salts like potassium permanganate and hydrazine sulphate on the thermal properties of the materials was also evaluated. Leaching studies were also performed on melt-densified specimens in the laboratory. The average leach index was observed to be around 9, which was higher than the minimum stipulated value.

High velocity compaction compared with conventional compaction

Compaction to full density is a means to deliver performance and precision without the distortion associated with sintering densification. High strain rate compaction using shock waves has been demonstrated as one means to attain full density in the green state. In the present study, variations in the compaction pressure are used to determine the conditions for attaining full density and these conditions are compared between high velocity and traditional die compaction technologies. A diminishing effect of compaction pressure on densification was observed. At the same compaction pressure the green density and hardness were lower using high velocity compaction. Sound velocity measurements in the powder show high velocity compaction did not generate a shock wave. Therefore, under subcritical compaction velocity conditions there is a higher green density from conventional compaction when compared using the same peak pressure.

Evaluating stiffness and strength of pavement materials

Current mechanical empirical-based pavement design requires use of the mechanical properties of pavement materials. For quantitative evaluations of the mechanical properties (i.e. stiffness and strength), field tests are emphasised. In this paper, a recently developed instrument called the soil stiffness gauge (SSG) and the dynamic cone penetrometer (DCP) have been used to assess respectively the in-situ stiffness and strength of natural earthen materials, industrial byproducts, and chemically stabilised soils from ten highway construction sites around the state of Wisconsin, USA. The SSG and DCP survey data were analysed to develop a relationship between the SSG stiffness and DCP penetration index (DPI) values for individual material types and for all materials combined. A simple linear semi-logarithmic model is obtained between the SSG stiffness and DPI values, with the coefficient of determination, R2, ranging from 0·47 to 0·75 for individual material types and an R2 value of 0·72 for all materials combined. The SSG stiffness and DPI values can be also correlated with the modulus (E) and California bearing ratio (CBR) of the materials respectively. A good relationship is obtained between E from the SSG and CBR from the DCP, and is compared with the well-known equations developed by Powell et al. and AASHTO as well as other available correlations from different in-situ tests: the falling weight deflectometer, German light drop weight, and plate load tests. Finally, the proposed power model is validated with a data set from two other test sites. Either or both devices show good potential for future use in pavement and subgrade materials evaluation. The in-situ stiffness and strength properties of various materials can be rapidly and directly monitored in companion with the conventional compaction control tests during pavement construction. The modulus of pavement and subgrade materials is uniquely related to CBRs regardless of soil type and site, and their relationship is also applicable to both as-compacted and post-construction states.

Magnetic Properties of Topochemically Sintered Barium Hexaferrite

This communication describes the method of topochemical reaction sintering for the production of barium hexaferrite. Topochemical reaction sintering overcomes crucial process steps that are used in the conventional wet magnetic compaction method, such as calcination, wet grinding, and wet magnetic compaction. Chemical reaction sintering of the above-mentioned ferrite has been performed in air and under vacuum. Barium hexaferrite that has been topochemically sintered in air at a temperature of 1473 K for 60 min shows a maximum magnetic energy product ((BH)max) of 6.56 kJ/m3, whereas barium hexaferrite that has been topochemically sintered at a temperature of 1423 K for 30 min under vacuum (10-2 mm Hg (∼0.133 Pa)) shows (BH)max= 7.6 kJ/m3. The variation of the magnetic properties of the topochemically sintered ferrites is interrelated to process variables such as temperature and sintering duration (time).

Characterization and dielectric properties of Sr4La2Ti4M6O30(M=Nb, Ta) ceramics

Sr4La2Ti4M6O30 (M=Nb or Ta) compounds were synthesized by the conventional powder compaction and high temperature solid state reaction technique. The dielectric properties of the sintered samples were measured and they were further characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Sr4La2Ti4M6O30 compounds are paraelectric phases adopting filled tetragonal tungsten–bronze (TB) structure at room temperature. Sr4La2Ti4Nb6O30 and Sr4La2Ti4Ta6O30 show high dielectric constants of 387 and 166 together with low dielectric loss of 0.0084 and 0.0042 at 1 MHz, respectively.

Reactive sintering in Fe-Co system

Low porosity powder metallurgy compacts have been manufactured from treated elemental iron and cobalt powders sintered at 1150°C under an H2(g) atmosphere. Their microstructures consist of an interconnected mixed oxide network which encapsulates both the iron and cobalt phases. The production technique employed is an innovative process termed reacto-thermitic sintering (RTS), which leads to near full density and near net shape parts utilising conventional uniaxial compaction and mesh belt furnace practices. The RTS technique relies on microscale exothermic reaction between small quantities of added elemental Al and oxides present on the surface of the bulk powder, together with the bulk powder itself. This results in the production of a transient liquid phase which freezes rapidly and consolidates the compact without slumping. In order to generate an interconnected mixed oxide network, experiments were designed such that the Al powder reacts with the cobalt and the surface of the iron powder which is artificially doped with Fe and Cr oxides.Differential thermal analysis (DTA) and energy balance calculations revealed that the Al and the oxide coating reaction does not proceed directly. Instead the main contribution to the exothermic process is the reaction between Al and Co/Fe. The system does not exhibit true RTS behaviour and the interconnected network of mixed Al, Cr, and Fe oxides is created by subsequent reaction of Co-Al and Fe-Al intermetallics with the artificial Fe-Cr oxide coating on the Fe. The microstructure obtained exhibits negligible porosity with the metallic particles on the whole fully encapsulated by the oxide.

Study on mechanical properties of warm compacted iron-base materials

Mechanical properties of the warm compacted iron-base powder metallurgy materials were compared with those of conventional cold compacted materials. Factors such as compaction temperature, lubricant concentration and lubricant’s property were studied. A lubricant for warm compaction powder metallurgy was developed. An iron-based powder metallurgy material with a green density of 7.31 g/cm3 (a relative density of 92.5%) can be obtained by pressing the powder at 700 MPa and 175 °C. The sintered materials have a density of 7.2 g/cm3, an elongation of 2.1% and a tensile strength of 751 MPa compared to 546 MPa using conventional cold compaction with the same lubricant and 655 MPa using warm compaction with other lubricant. Compact density and mechanical properties were influenced strongly by the compacting temperature. Although the best quality compacts can be obtained at 175 °C, warm compaction within 165 to 185 °C can give high density compacts. Evidence shows that compact density depends on the friction coefficient of the lubricant.

Residual Stresses in Green Bodies of Steel Powder after Conventional and High Speed Compaction

Residual stresses have been measured in green bodies after conventional compaction at 400 and 530 MPa and after high speed compaction with impact energies of 1400J and. 2200J. The former were recta ...

Studies of residual stress, microcracks, hardness and microstructure of cold compacted metallic green bodies

ABSTRACTThe residual stresses have been measured by X-ray and neutron diffraction on PM green bodies manufactured by conventional and high speed compaction of iron powder with and without added copper and brass powder. Compressive residual stresses are present in a thin layer in both top and side surfaces. They are largest in the side surfaces due to plastic deformation of the surface material caused by the friction forces during ejection out of the die. In the interior of the green body residual stresses exist with certain region under compression (periferical regions) and other under tension (more central regions). It is unclear whether mixing iron powder with brass or copper powder leads to considerable phase stresses between the two phases.

Reactive sintering of stainless steel

Pressed and sintered 316L type stainless steel compacts have been produced using an innovative process termed reactothermitic sintering RTS. This technique has the ability to produce full density, near net shape parts using conventional compaction and mesh belt furnace practices. It utilises chemical reactions at the surface of the stainless steel powders in which the energy balance is matched to provide transient liquid films that can be frozen at high cooling rates to consolidate the material without slumping. Small quantities of elemental aluminium and nickel powders are added before compaction that react, during sintering, both with themselves and with oxide layers present on the bulk stainless steel powder surfaces. In addition to the naturally occurring oxides present on the surface of stainless steel powders, artificial oxide layers, deposited by sol-gel and direct thermal oxidation, have been used to aid investigations into the nature of the reactions involved. The RTS technique leads to the generation of novel microstructures in the systems described that are characterised by negligible interconnected porosity. The present paper details the experimental programme undertaken to ascertain and substantiate these phenomena together with a model of how porosity is eliminated in this system.

Dielectric and ferroelectric properties of Ba3M3Ti5Nb5O30 (M = Sm or Y) ceramics

$$Ba_3 M_3 Ti_5 Nb_5 O_{30}$$ (M=Sm or Y) compounds were synthesized by the conventional powder compaction and high temperature solid state reaction technique. The calcined compounds were pelletized and sintered in the range 1275–1325 °C for 4 h. The dielectric and ferroelectric properties of the sintered pellets were measured and further characterised by X-ray diffraction and scanning electron microscopy (SEM). Sm and Y substituted compounds were found to have tetragonal structure and shown dielectric constants of 145 and 49 respectively at 1 MHz. The dielectric loss increases with frequency. Samarium compound had undergone a diffuse phase transition in the temperature range 195–210 °C whereas the same with Yttrium had shown the transition at around 25 °C.

Self-diffusion and magnetic properties in explosion densified nanocrystalline Fe

The enhanced diffusivity due to the high volume fraction of grain boundaries (GB's) is a key feature for the modified physical and chemical properties of nanocrystalline (n-) materials in contrast to the chemically identical coarse-grained solids. The authors previously performed tracer diffusion experiments on high-density n-Pd (relative density {rho}/{rho}{sub 0} {approximately} 97%, where {rho}{sub 0} is the theoretical density) and n-Fe ({rho}/{rho}{sub 0} {approximately} 92%) prepared by conventional static compaction of the gas-condensed powders at elevated temperatures, showing that the diffusivity of the n-metals is similar to the conventional GB diffusion in polycrystalline (poly-) metals. The specimens used in these studies, however, were not fully dense, with defects such as pores or cracks which may act as fast diffusion paths. The dynamic compaction technique utilizing the explosion or collide of a high speed projectile has also been applied for consolidation of fine powders of metals and ceramics. Recently, n-ceramics prepared by static pressing of fine powders were successfully further densified to more than 90% of the theoretical density by explosive compaction suppressing grain growth and contamination. In order to provide additional experimental information on interface structure and properties in n-metals, the density of n-Fe was further increased by explosive compactionmore » and effects of the densification on both self-diffusivity and bulk magnetic properties were examined.« less

Density Gradients in Multilayer Compacted Iron Powder Parts

The use of multilayer compaction to form powder metal (P/M)components, is encouraging. With this process, a part is formed by successively compacting layers of powder. The formation of parts with larger than conventional height to diameter ratios is possible. Multilayer compaction also reduces the density gradients normally observed in large parts from conventional double action compaction. Optimization of the layer thickness based on the powder characteristics can lead to greatly reduced density gradients. The physical properties of multilayer compacted components are investigated as a function of layer thickness. The research has been performed with two iron powders of varying characteristics. The compressibility of the powder versus the layer thickness is discussed and related to the density distribution in the component.

Partitionable multistage interconnection networks. Part 2: Task migration schemes

A new subcube migration scheme for maximally utilizing system resources is proposed for multiprocessor systems based on multistage interconnection networks (MINs). The objective is to migrate tasks to create larger free subcubes; this is referred to as subcube migration. After the migration, we can then apply the more conventional subcube compaction schemes. First, the problem formulation is presented and the goals are set for the solution. It is shown that the migration problem is, in fact, not just a one subcube to one subcube migration problem (as treated in the previous work), but rather a many subcubes to many subcubes migration problem. This problem analysis and formulation lead us to a sophisticated subcube migration scheme. This scheme, thus, successfully handles many?to?many subcube migrations. It is not only near?optimal but also scalable for different sizes of the multiprocessors. Extensive experiments were performed over a wide range of load distributions and problem sizes; the results show that for problems sizes of all practical purposes, the proposed scheme achieves very high system utilization, while requiring little computing time.

Speech compaction using temporal decomposition

A new method for compacting speech in the time domain is proposed. Unlike conventional time scale modification techniques, the method emphasises event locations, obtained from spectral analysis and hierarchical temporal decomposition, and removes the remaining parts of the signal adaptively. Subjective evaluation tests show that the new method outperforms conventional compaction methods from the viewpoints of quality and comprehensibility of the compacted signal.

Hot compaction and consolidation of polycarbonate powder

AbstractIn order to take advantage of the potential benefits provided by solid‐state processing of thermoplastic polymers (1–3), conventional compaction and sintering techniques must be modified to prevent large‐scale recovery (or dimensional changes) that occur upon heating polymeric compacts above their respective glass transition temperature (Tg). Two solid‐state processing techniques that have the potential for reducing recover, hot compaction and consolidation (sintering polymeric compacts under applied pressure), were investigated in this study. The results presented in this paper show that while hot compaction (below Tg) does not prevent large‐scale recovery, consolidation using pressures as low as 50 kPa (7.3 psi) did significantly reduce recovery in polycarbonate compacts.

Higher green strength and improved density by conventional compaction : S.H.Luk et al. (Hoeganaes Corp. Riverton, USA.)

Higher green strength and improved density by conventional compaction : S.H.Luk et al. (Hoeganaes Corp. Riverton, USA.)

Compaction Curves on Volume Basis

Abstract The compaction curves of soils are generally expressed in terms of dry density and water content. While this representation serves well to compare the efficiency of compaction of different soils whose specific gravities lie in a narrow range (2.6 to 2.7), it fails for materials of varying specific gravities. It has been shown that for fly ashes with a wide range of specific gravities the degree of compaction of different fly ashes cannot be compared from conventional compaction parameters. Compaction curves expressed on a volume basis, viz., volume of solids per unit volume of compacted sample or porosity or void ratio and volume of water per unit volume of solids, can better serve to explain the compaction. Further, it has been shown that for fly ashes of different specific gravities only compaction parameters expressed on a volume basis can be interrelated.